The Animal Barrier Shared Resource (ABSR) supports the mission of the AECC by providing an environment in which the highest quality of animal research studies can be conducted while maintaining the highest standards of animal care and animal welfare. A major objective of the ABSR is to maintain the health quality of barrier housed specific pathogen-free (SPF) mice, keeping them free of adventitious murine infectious agents that could disrupt breeding or confound research results. Barrier housing is provided for SPF mice while permitting supervised access for investigators. AECC investigators maintain breeding colonies either to expand novel strains bearing transgene or targeted mutations from genetically-manipulated founder animals, or to recombine several specific alleles from different genetic loci into a limited set of genotypes on a single strain background. Frequent convenient access is crucial for investigators so that they may set up matings, collect tissue biopsies from successive litters for genotype determination, and observe animals for physical and behavioral characteristics (phenotype), specifically, their propensity to develop neoplasia. In addition, many AECC investigators use specific pathogen-free rodents that either have a genetic predisposition to develop spontaneous neoplasia or are immunodeficient and tolerate tumor xenografts as models to study specific processes such as angiogenesis and metastasis and for testing antineoplastic therapies. These investigators must have frequent access to their animals to implant tumor tissues, monitor tumor growth, administer various treatments, and collect tissue biopsies. Animal husbandry services, veterinary care, and comprehensive rodent quality assurance and quarantine programs are provided to the AECC by the Institute of Animal Studies (IAS). The IAS consists of three faculty Laboratory Animal Veterinarians (including the Director), three Veterinary Technicians, a staff of approximately 40 Animal Caretakers, a Facilities Manager, two Husbandry Supervisors, as well as office administrative staff. In addition to providing veterinary care, the IAS veterinarians also provide oversight of the animal care and use program, monitor regulatory compliance, and conduct small-group and individual training sessions for investigators. Pathology diagnostic services are provided by a Veterinary Pathologist who also directs the Histopathology Shared Resource.